Hybrid vehicles using drive power obtained from a motor generator as vehicle propulsion power are commonly provided with a rechargeable (chargeable/dischargeable) secondary battery used during operation. Electric power accumulated in this secondary battery is converted into drive electric power by an inverter circuit and then extracted to drive the above motor generator, while the secondary battery is charged by the generated electric power. Since such a secondary battery has an internal resistance, charge/discharge involves heat generation. Accordingly, as charge/discharge of the secondary battery is repeated, the temperature of the secondary battery rises.
Also, generally, continuous use of such a secondary battery in a high-temperature state contributes to shortening of the life of the battery. Accordingly, in order to protect the secondary battery, charge/discharge current is limited when the temperature of the secondary battery is high. As a result, sufficient vehicle propulsion power cannot be obtained, and, in a case of a hybrid vehicle, the fuel mileage is reduced.
In consideration of this problem, hybrid vehicles are commonly provided with a cooling fan for cooling the secondary battery. Generally, as the charge/discharge current of secondary battery increases, the rise of temperature of secondary battery becomes larger. Accordingly, as illustrated in FIG. 7, as the amount of charge/discharge of secondary battery increases, a larger cooling air volume flow is required.
On the other hand, in a hybrid vehicle, generally, when the vehicle interior background noise is kept at a low level, such as while parking or running at a low speed, the amount of charge/discharge of secondary battery is also small, so only small air volume flow of cooling fan is required; when the vehicle interior background noise is large, such as running at a high speed, the amount of charge/discharge of secondary battery is also large. Thus, in Japanese Patent Laid-Open Publication No. 2004-48981, there has been proposed a control device which, as illustrated in FIG. 6, performs control of reducing cooling air volume flow according to the line of background noise Level 1 when the vehicle interior background noise is low while running at a low speed, and of increasing air volume flow according to the line of vehicle interior background noise Level 2 or 3 when the vehicle interior background noise is high while running at a high speed, and thereby cools effectively the secondary battery without increasing recognized noise from cooling fan. Also, as the temperature level of the secondary battery increases, a larger cooling air volume flow is required for the secondary battery. Thus, in Japanese Patent Laid-Open Publication No. 2004-48981, there has also been proposed a technique in which, as illustrated in FIG. 6, control is performed so as to increase the air volume flow of secondary battery cooling fan as the temperature level of secondary battery rises.
However, according to the above-noted secondary battery cooling control, when a rapid change from a low-speed running state to acceleration is desired, since the air volume flow of cooling fan has been suppressed low in the interest of noise within vehicle, there arises a problem that the amount of charge/discharge of secondary battery is limited to prevent an excessive rise of secondary battery temperature and thus an output required for acceleration cannot be obtained from the motor generator. Particularly, when “sporty” driving is desired, such as on a mountain road or the like, there arises a problem that it is sometimes impossible to achieve sufficient acceleration performance as a result of the control suppressing the cooling fan noise. On the other hand, improvement of drive power performance is sometimes desired by an operator more than low noise within the vehicle.
In consideration of this, the present invention advantageously provides a control device capable of achieving larger drive power performance without causing a cooling fan to limit the amount of charge/discharge of secondary battery when an operator values improvement of drive power performance higher than reduction of noise within the vehicle.